Top electrode etch in a magnetoresistive device and devices manufactured using same

ABSTRACT

A two-step etching process is used to form the top electrode for a magnetoresistive device. The etching chemistries are different for each of the two etching steps. The first chemistry used to etch the top portion of the electrode is more selective with respect to the conductive material of the top electrode, thereby reducing unwanted erosion of the photoresist and hard mask layers. The second chemistry is less corrosive than the first chemistry and does not damage the layers underlying the top electrode, such as those included in the magnetic tunnel junction.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/296,181 filed Jun. 4, 2014 and claims priority to thatapplication as well as U.S. Provisional Application No. 61/941,250 filedFeb. 18, 2014. The contents of these applications are incorporated byreference herein in their entirety.

TECHNICAL FIELD

The disclosure herein relates generally to magnetoresistive devices andmore particularly to the use of spacer layers in such devices andmethods for manufacturing such devices, including using non-reactivematerials to strip photoresist.

BACKGROUND

Resistive memory devices store information by varying the resistanceacross the memory device such that a read current through a memory cellin the memory device will result in a voltage drop having a magnitudethat is based on the information stored in the memory cell. For example,in certain magnetic memory devices, the voltage drop across a magnetictunnel junction (MTJ) can be varied based on the relative magneticstates of the magnetoresistive layers within the memory cell. In suchmemory devices, there is typically a portion of the memory cell that hasa fixed magnetic state and another portion that has a free magneticstate that is controlled to be either parallel or antiparallel to thefixed magnetic state. Because the resistance through the memory cellchanges based on whether the free portion is parallel or antiparallel tothe fixed portion, information can be stored by setting the orientationof the free portion. The information is later retrieved by sensing theorientation of the free portion. Such magnetic memory devices are wellknown in the art.

Writing magnetic memory cells can be accomplished by sending aspin-polarized write current through the memory device where the angularmomentum carried by the spin-polarized current can change the magneticstate of the free portion. One of ordinary skill in the art understandsthat such a current can either be directly driven through the memorycell or can be the result of applying one or more voltages where theapplied voltages result in the desired current. Depending on thedirection of the current through the memory cell, the resultingmagnetization of the free portion will either be parallel orantiparallel to the fixed portion. If the parallel orientationrepresents a logic “0”, the antiparallel orientation may represent alogic “1”, or vice versa. Thus, the direction of write current flowthrough the memory cell determines whether the memory cell is written toa first state or a second state. Such memory devices are often referredto as spin torque transfer memory devices. In such memories, themagnitude of the write current is typically greater than the magnitudeof a read current used to sense the information stored in the memorycells.

Manufacturing magnetoresistive devices, including MTJ devices, includesa sequence of processing steps during which many layers of materials aredeposited and then patterned to form a magnetoresistive stack and theelectrodes used to provide electrical connections to themagnetoresistive stack. The magnetoresistive stack includes the variouslayers that make up the free and fixed portions of the device as well asone or more dielectric layers that provide at least one the tunneljunction for the MTJ device. In many instances, the layers of materialare very thin, on the order of a few or tens of angstroms. Similarly,the dimensions of such layers after patterning and etching are extremelysmall, and small deviations or imperfections during processing can havea significant impact on device performance.

Because an MRAM device may include millions of MTJ elements, preciseprocessing steps used in manufacturing the devices can contribute toincreased densities by allowing devices to be placed in close proximitywithout unwanted interaction. Therefore, it is desirable to providetechniques for manufacturing such devices that ensure proper operationwhile supporting increased densities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 and 5-8 illustrate cross-sectional views of layers included ina magnetoresistive device during different stages of manufacturing inaccordance with an exemplary embodiment;

FIG. 4 illustrates a cross-sectional view of layers included in amagnetoresistive device during definition of a top electrodemanufactured using a single step etching process;

FIG. 9 illustrates a cross-sectional view of a set of layers included ina magnetoresistive device in accordance in accordance with an exemplaryembodiment;

FIG. 10 illustrates a cross-sectional view of a set of layers includedin a magnetoresistive device in accordance in accordance with anotherexemplary embodiment;

FIGS. 11-14 are flow charts of methods of manufacturing amagnetoresistive device in accordance with exemplary embodiments;

FIGS. 15-21 illustrate cross-sectional views of layers included in amagnetoresistive device during different stages of manufacturing inaccordance with another exemplary embodiment;

FIGS. 22 and 23 are flow charts of methods of manufacturing amagnetoresistive device in accordance with exemplary embodiments;

FIGS. 24A and 24B are a flow chart of a method of manufacturing amagnetoresistive device in accordance with another exemplary embodiment;and

FIGS. 25-27 are flow charts of methods of manufacturing amagnetoresistive device in accordance with exemplary embodiments.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. Any implementation describedherein as exemplary is not necessarily to be construed as preferred oradvantageous over other implementations.

For simplicity and clarity of illustration, the figures depict thegeneral structure and/or manner of construction of the variousembodiments. Descriptions and details of well-known features andtechniques may be omitted to avoid unnecessarily obscuring otherfeatures. Elements in the figures are not necessarily drawn to scale:the dimensions of some features may be exaggerated relative to otherelements to improve understanding of the example embodiments. Forexample, one of ordinary skill in the art appreciates that thecross-sectional views are not drawn to scale and should not be viewed asrepresenting proportional relationships between different layers. Thecross-sectional views are provided to help illustrate the processingsteps performed by simplifying the various layers to show their relativepositioning. Moreover, while certain layers and features are illustratedwith straight 90-degree edges, in actuality or practice such layers maybe more “rounded” or gradually sloping.

The terms “comprise,” “include,” “have” and any variations thereof areused synonymously to denote non-exclusive inclusion. The term“exemplary” is used in the sense of “example,” rather than “ideal.”

During the course of this description, like numbers may be used toidentify like elements according to the different figures thatillustrate the various exemplary embodiments.

For the sake of brevity, conventional techniques related tosemiconductor processing may not be described in detail herein. Theexemplary embodiments described herein may be fabricated using knownlithographic processes as follows. The fabrication of integratedcircuits, microelectronic devices, micro electro mechanical devices,microfluidic devices, and photonic devices involves the creation ofseveral layers of materials that interact in some fashion. One or moreof these layers may be patterned so various regions of the layer havedifferent electrical or other characteristics, which may beinterconnected within the layer or to other layers to create electricalcomponents and circuits. These regions may be created by selectivelyintroducing or removing various materials. The patterns that define suchregions are often created by lithographic processes. For example, alayer of photoresist is applied onto a layer overlying a wafersubstrate. A photo mask (containing clear and opaque areas) is used toselectively expose the photoresist by a form of radiation, such asultraviolet light, electrons, or x-rays. Either the photoresist exposedto the radiation, or that not exposed to the radiation, is removed bythe application of a developer. An etch may then be applied to theunderlying layer not protected by the remaining resist such that thelayer overlying the substrate is patterned. Alternatively, an additiveprocess can be used in which a structure is built up using thephotoresist as a template.

There are many inventions described and illustrated herein, as well asmany aspects and embodiments of those inventions. In one aspect, thedescribed embodiments relate to, among other things, methods ofmanufacturing a magnetoresistive-based device having one or moreelectrically conductive electrodes or conductors on either side of amagnetic material stack. As described in further detail below, themagnetic material stack may include many different layers of material,where some of the layers include magnetic materials, whereas others donot. In one embodiment, the methods of manufacturing include forming thelayers for the magnetoresistive device and then masking and etchingthose layers to produce a magnetic tunnel junction (MTJ) device.Examples of MTJ devices include transducers such as electromagneticsensors as well as memory cells.

Magnetoresistive devices are typically formed to include a top electrodeand a bottom electrode that permit access to the device by allowing forconnectivity to other circuit elements. Formation of these electrodesduring the processing operations used in manufacturing the devices canbe optimized in order to provide sharp definition of the electrodesthereby both aiding in defining and producing other layers included inthe magnetoresistive device structure as well as providing knowndimensions for the magnetoresistive device structure, thereby enablingsuch devices to be placed in close proximity to each other. By enablingthe devices to be placed in close proximity to each other, devicedensities in applications such as MRAMs can be increased. One techniquedescribed in more detail below uses a two-step etching process to definethe top electrode within the device. In one embodiment, the two-stepetching process uses a combination of isotropic and more anisotropicetching, where the different levels of isotropy can be achieved byvarying the power applied during plasma etching as well as varying thepressure applied during such plasma etching. In another embodiment, thetwo-step etching process uses different etching chemistries for thesteps, where the top portion of the electrode is etched using a moreselective etching chemistry, whereas the bottom portion uses aless-corrosive chemistry that may not be as selective.

Another technique described herein provides for non-reactive strippingof the photoresist used to pattern the top electrode. For example, thephotoresist may be stripped using water vapor or some othernon-oxidizing gas, where such non-reactive stripping may also providepassivation with respect to other layers included in themagnetoresistive device structure. By using a non-reactive strippingprocess, oxidation of exposed material, such as the sidewalls of the topelectrode, is avoided. Avoiding oxidation of those sidewalls helpsretain more precise physical definition of the magnetoresistive device,thereby ensuring proper operation within tight specifications.

Another technique that helps further more precise magnetoresistivedevice physical definition, and thereby promote higher densities withless operational deviation between devices, is to optimize the materialused for a spacer layer included within the magnetoresistive devicestructure. As discussed in more detail below, a spacer layer can helpprevent diffusion between different layers within the magnetoresistivedevice. When the spacer layer comprises material that can oxidize,subsequent etching steps following definition of the spacer layer canresult in sidewalls of the spacer layer oxidizing, thereby causingsidewall roughness or bulging that negatively impacts the physicaldefinition of the underlying MTJ layers. Thus, embodiments arecontemplated in which the material used for the spacer layer isnon-reactive such that it does not oxidize or react with etchchemistries used in defining the layers below the spacer layer in themagnetoresistive device. In other embodiments, the spacer layer isomitted entirely, thereby ensuring that undesirable sidewall roughnessdue to spacer layer oxidation does not occur.

FIG. 1 illustrates a cross-sectional view of a partially formedmagnetoresistive device disposed on a substrate 102. The cross-sectionalview shows a plurality of layers, where each of the layers is formed,deposited, grown, sputtered, or otherwise provided. The layers may bedeposited using any technique now known or later developed. Thesimplified cross-sectional view presented in FIG. 1 includeselectrically conductive layer 110, a plurality of layers 118 making upthe magnetoresistive stack corresponding to the magnetoresistive device,electrically conductive layer 150, hard mask layer 160, and patternedphotoresist layer 170. The patterned photoresist layer 170 may bedeposited and patterned using any technique now known or laterdeveloped, for example, well known conventional deposition andlithographic techniques.

The electrically conductive layers 110 and 150 provide the material usedto define the top and bottom electrodes for the magnetoresistive device.The plurality of layers 118 within the magnetoresistive stack mayinclude a number of different layers of both magnetic and nonmagneticmaterial. For example, the plurality of layers 118 may include multiplelayers of magnetic material, dielectric layers that provide one or moretunnel barriers or diffusion barriers, coupling layers between layers ofmagnetic material that provide for ferromagnetic or antiferromagneticcoupling, anti-ferromagnetic material, and other layers utilized inmagnetoresistive stacks as currently known or later developed. Forexample, the plurality of layers 118 may include a first set of layersforming a synthetic antiferromagnetic structure (SAF), a dielectriclayer forming a tunnel barrier, another set of layers forming asynthetic ferromagnetic structure (SYF), another dielectric layerforming a diffusion barrier, and one or more layers forming a spacerlayer. Notably, each of the layers included in the magnetoresistivedevice may be a composite layer that includes multiple sub-layers. Otherembodiments may include multiple SAFs, SYFs, and tunnel barriers inaddition to the other layers, where the materials and structures arearranged in various combinations and permutations now known or laterdeveloped.

One technique described herein focuses on a two-step etching processused to define the top electrode from the electrically conductive layer150. Because the top electrode overlies the stack for themagnetoresistive device, the benefits of the two-step etching processwould be applicable to various magnetoresistive devices having differentstack compositions.

In FIG. 2, the cross-sectional view of FIG. 1 is updated to reflect thetrimming of the patterned layer of photoresist 170 to produce trimmedphotoresist 172. After initially patterning the photoresist to producethe patterned photoresist layer 170, it may be advantageous to “trim”the photoresist and thereby adjust or shrink the size of at least aportion of the magnetoresistive device that is defined at least in partby the photoresist. The trimming process may also provide patternfidelity that can result in more uniform edges for the device structure.The photoresist 120 may be trimmed using any technique now known orlater developed, for example, well known conventional trimmingtechniques.

FIG. 3 shows the cross-sectional view following etching of the hard masklayer 160 to produce a hard mask 162. As used herein, “hard” when usedwith “hard mask” means the ability to resist a particular etch. The hardmask layer 160 may be etched via chemical etching to form or provide thehard mask 162. Examples of such chemical etch processes including thoseusing gases such as CF₄, CHF₃, CH₂F₂ and carrier gases such as Ar andXe. Notably, the hard mask layer 160 may be etched, formed and/orpatterned using any etchants and techniques now known or laterdeveloped—for example, using conventional etchants and techniques.

FIG. 4 shows the cross-sectional view from FIG. 3 following a one-stepetch using a constant bias power and a single etching chemistry. Biaspower refers to a voltage applied to a chuck upon which the wafer sitsin the etching chamber, where the voltage applied directs the plasma inthe etching chamber. For example, a higher power (greater voltage) maycause the plasma to be attracted to the chuck, thereby causing theetching operation to become more anisotropic as the plasma is directedin a more downward direction. During etching of the top electrode, itmay be desirable to also realize a benefit in shrinking the footprint ofthe trimmed photoresist 172. Thus, while the photolithography equipmentinitially used a pattern the photoresist layer 170 may have certainlimitations, subsequent trimming can reduce the minimum feature size ofthat photolithography equipment, and isotropic etching may be used tofurther trim the photoresist 172. Isotropic etching results in materialremoval in a non-direction-specific format. Thus, the top surface of thetrimmed photoresist 172 will be etched along with the sidewalls of thetop electrode 152. In contrast to isotropic etching, anisotropic etchinghas directional dependence. Thus, if a more anisotropic etch is applied,such as one that is directed vertically from top to bottom, morematerial will be removed from the top of the trimmed photoresist 172than will be removed from the sidewalls.

As depicted in FIG. 4, using a one-step etch with constant isotropy andetching chemistry for the formation of the top electrode can result innon-uniform etching of the electrically conductive layer 150 to produceetched electrically conductive portion 152 which includes undesirableresidual portions 151. The undesirable residual portions 151 maynegatively impact subsequent etching steps directed at the layersunderlying the electrically conductive layer 150. Thus, a two-step etchwith different isotropy for each step helps in eliminating theundesirable residual portions 151. The isotropic step of the two stepetch provides the necessary “trim” while the anisotropic part removesresidual portions 151.

In order to avoid the potential issues illustrated and described withrespect to FIG. 4, the etching of the top electrode can be split intotwo separate steps. The two steps may be referred to as the main etchand the over etch. By separating the etching into two steps, andproviding for different levels of isotropy within those two steps, thedesired effects of isotropic etching can be realized along with thedesired effects of more anisotropic etching. In one embodiment, the mainetch is an isotropic etch, whereas the over etch is more anisotropic inorder to provide the sharp features desirable for the top electrode asit may be used as a reference for subsequent etching steps and overalldevice definition. In another embodiment, the main etch may be moreanisotropic, thereby providing an initial sharp feature definition, andthe over etch may be isotropic, thereby providing the benefitsassociated with a non-direction-specific etch.

The electrically conductive layer 150 from which the top electrode isformed may include one or more layers of electrically conductivematerial such as, for example, Ta, TaN or Ta—TaN composite. In oneembodiment, a Ta, TaN or Ta—TaN composite electrically conductive layer150 may be of a thickness of about 50-1000 Angstroms. The etchants andtechniques used to etch those materials in the two-step etching processmay be any etchants or techniques now known or later developed. Examplesinclude chemical etch processes with gases such as Cl₂, CF₄, CHF₃, CH₂F₂and carrier gases such as Ar, N₂ and Xe. Different gases may be usedduring the main etch and the over etch to achieve the desired result.For example, a Cl₂-based chemistry may be used for the main etch and aF₂-based etch chemistry may be used for the over etch. As described infurther detail below, specific embodiments are contemplated in which theetching chemistries used in each portion of the two-step etch areselected to improve device manufacturing, where, in some embodiments thelevel of anisotropy used with respect to each of the different etchingchemistries is the same, whereas in others the level of anisotropy isdifferent.

In order to control the level of isotropy associated with the particularetch process, the power applied to the chuck on which the semiconductorwafer sits during etching can be varied in order to increase or decreasethe vertical flow of etching material within the etching chamber. Forexample, applying higher power to the chuck can result in plasma withinthe chamber being attracted towards the chuck, thereby causing it toimpact the material on the wafer in a more directional, verticalfashion. Applying lower power would reduce such directional flow,thereby increasing the isotropy of the etching process. In addition tovarying the power for the etch, the pressure applied within the chamberduring the etch can also impact the level of isotropy. Lower pressurewithin the chamber allows the etching material to move more freely,thereby allowing increased power to have a greater impact on thedirectional flow of the etching material. Greater pressure producesgreater isotropy as the pressure causes the particles of etchingmaterial to be forced against the material being etched more evenly fromall directions. The isotropy of the etch may be controlled using anytool technique now known or later developed. In other embodiments,rather than using the same etching material with different power orpressure settings, the two-step etch process can be accomplished byusing two separate etching materials, where one etching material is moreanisotropic than the other.

FIG. 5 illustrates a cross-sectional view corresponding to FIG. 3 afteran initial main etch has been performed. Thus, rather than having asingle step etch process for defining the top electrode such as thatdiscussed with respect to FIG. 4, FIG. 5 illustrates the cross-sectionalview following the first step of a two-step etching process used todefine the top electrode. In one example, the initial main at may be anisotropic etch, thereby further reducing the feature size of thepatterned photoresist 172. Thus, while not illustrated in FIG. 5, thewidth and the height of patterned photoresist 172 may shrink during theinitial main etch due to the isotropic nature of the main etch. Theinitial main etch may be a low-power etch that moves more slowly throughthe material within the electrically conductive layer 150. Following themain etch, the remaining portion of the electrically conductive layer154 still includes portions 153 that need to be removed in order tofully define the top electrode. Determining when to stop the main etchmay be based on a preset time or based on detection of an endpointwavelength using optical emission spectroscopy. Optical emissionspectroscopy can be used to detect when the spectrum corresponding tomaterial of the electrically conductive layer begins to fall, therebyindicating that the main etch has almost reached the bottom of the layerof electrically conductive material.

While the main etch may provide the isotropic etching desired to furtherreduce the feature size of the patterned magnetoresistive device, theover etch may be more anisotropic in nature in order to provide astraighter profile for the magnetoresistive device and to help clearaway residual material left over from previous processing steps. Thus,the main etch may be use a lower power bias and be primarily isotropic,whereas during the over etch, the power bias is raised to make theetching more anisotropic. For example, the main etch may be completelyisotropic, whereas the over etch is 80% isotropic and 20% anisotropic.In a specific example using an Applied Materials 200 mm DPS chamber, themain etch may utilize about 50-60 W of power for the bias, whereas theover etch increases the power by about 50 percent.

FIG. 6 illustrates a cross-sectional view following the over etch. Asshown, the over etch removes the remaining portions 153 of theelectrically conductive layer 150 that are not a part of the topelectrode 155. Thus, the top electrode 155 depicted in FIG. 6 has beenproduced using the two-step etch such that the sharper sidewalls areachieved by more anisotropic etching, while still achieving the benefitsassociated with an isotropic main etch. In an embodiment where themagnetoresistive device is a memory cell included in a memory device,the anisotropic etching decreases variations in certain parameters forthe large number of memory cells included in the memory device. Beingable to provide sharp well-defined device structures reduces variationsin parameters such as resistance, switching field, and switchingvoltages associated with the memory cells making up the memory device.

As shown in FIG. 6, the over etch stops prior to reaching the pluralityof layers 118 that are subsequently processed to form themagnetoresistive device stack. In some embodiments, the top layers ofthe plurality of layers 118 may benefit from the etching characteristicsof the over etch used to finalize the top electrode, and in such cases,the over etch may continue into one or more of the layers included inthe plurality of layers 118. However, in other cases, the higher powerover etch may be incompatible with the layers included in the pluralityof layers 118, and, in such cases, the over etch is stopped before itreaches those layers. For example, while the over etch may be a reactiveetch, a spacer layer at or near the top of the plurality of layers 118may require a non-reactive etch. As is the case with the over etch andother etching steps discussed herein, determining when the junctionbetween the layers has been reached and that it is time to stop etchingmay be based on an elapsed period of time or based on detection of anendpoint wavelength using optical omission spectroscopy.

In other embodiments, the top electrode etching may be accomplished by atwo-step etch in which the etching chemistry of each of the two steps isselected to minimize unwanted damage to certain layers while ensuringproper etching of other layers. For example, certain photoresist andhard mask layers may be susceptible to erosion by non-selective etchingchemistries. As such, if such non-selective etching chemistries are usedduring the main etch (e.g. as illustrated FIG. 5), erosion of thepatterned photoresist 172 and hard mask 162 may alter the resultingshape or composition of the top electrode, thereby causing contactissues in which electrical contact to the underlying MTJ is compromised.In such a situation, using a highly-selective etching chemistry that isselective with respect to the material in the electrically conductivelayer 150 allows the portions of that layer not part of the topelectrode to be removed while reducing unwanted erosion of the patternedphotoresist 172 and hard mask 162. Such a selective etching chemistryfavors removal of certain materials (i.e. is selective with respect toremoving those materials) over the removal of other materials. Forexample the selective etching chemistry used during the main etch mayremove material in the electrically conductive layer 150 while noteroding the patterned photoresist 172 and hard mask 162. Such aselective etching chemistries include more corrosive etching chemistriessuch as chlorine-based etching chemistries (e.g. Cl₂) and hydrogenbromide (HBr). In some embodiments, the etching chemistry used duringthe main etch may have an etch rate for the electrically conductivelayer 150 that is at least three times greater than the etch rate theetching chemistry has for the patterned photoresist 172 and hard mask162.

Corrosive, selective etching chemistries such as those including Cl₂ andHBr can damage the layers underlying the layer of conductive material150 from which the top electrode is formed. As such, instead of relyingon the same etching chemistry for the main etch and the over etch, aless corrosive etching chemistry can be used for the over etch, therebyavoiding damage to layers underlying the layer of conductive material.As such, the top electrode etch may be split into two portions, where afirst etching chemistry is used to etch the first portion of the layerof conductive material 150 and a second etching chemistry is used toetch the second portion of the layer of conductive material 150. In someembodiments, the first portion is larger than the second portion suchthat a majority of the etching of the layer of conductive material 150is performed using the first etching chemistry, which, as noted above,may be a more corrosive etching chemistry that is selective towards thematerial in the layer of conductive material. As is the case with atwo-step etch having different levels of anisotropy, the main etch maystop based on a predetermined amount of time passing or detection of anendpoint wavelength associated with the optical omission spectrum forthe etching operation.

During the second portion of the etching used to define the topelectrode (i.e. the over etch), a less corrosive etching chemistry maybe used to remove any remaining unwanted portions of the layer ofconductive material 150. As shown in FIGS. 5 and 6, the over etchremoves the remaining portions 153 of the electrically conductive layer150 that are not a part of the top electrode 155. In an embodiment inwhich a second etching chemistry is used for the over etch that isdifferent than that which is used for the main etch, a less corrosivechemistry may be used for the second portion to ensure than the layers118 underlying the top electrode 155 are not damaged. As noted above,corrosive chemistries such as Cl₂ and HBr may damage the underlyinglayers, and therefore using a less-corrosive etching chemistry to removeany remaining unwanted portions 153 of the electrically conductive layer150 during the over etch can avoid damaging those underlying layers 118.Examples of such less-corrosive etching chemistries include fluorinebased chemistries such as CHF₃, CF₄, and C₄F₈.

Such less-corrosive chemistries used for the over etch may also be lessselective with respect to the patterned layer of photoresist 172 andhard mask 162. However, because the over etch only removes a portion ofthe electrically conductive layer 150, the exposure of the photoresistand hard mask to the second etching chemistry is limited such thatunwanted erosion of those layers is also limited to tolerable levels. Asdiscussed above with respect to other etching steps, the over etch maystop based on a predetermined amount of time passing or detection of anendpoint wavelength associated with the optical omission spectrum forthe etching operation.

In yet other embodiments, more than two etching steps may be used todefine the top electrode 155, where the different etching steps mayinclude differing levels of anisotropy as well as differing chemistries.For example, a three-step etch may include a first main etch having afirst level of anisotropy and a first etching chemistry, a second mainetch having a second level of anisotropy and second etching chemistry,and an over etch having a third level of anisotropy and a third etchingchemistry. More specifically, the first main etch may use a generallyisotropic etch using a highly selective chlorine based chemistry, thesecond main etch may use a generally anisotropic etch using a slightlyless selective chemistry, and the over etch may be a anisotropic etchusing a non-corrosive chemistry.

Following definition of the top electrode 155, the patterned photoresist172 depicted in FIG. 6 may be stripped prior to further processing ofthe magnetoresistive device structure. In one embodiment, thephotoresist is stripped using water vapor or a different non-reactivegas. Stripping the photoresist can help to avoid problems that occurduring subsequent etching steps in which the photoresist would breakdown and result in undesirable residual material. For example, asubsequent etch using a mixture of Ar and O₂ gases may be adverselyaffected if the photoresist is not stripped away before performing thatetch.

FIG. 7 depicts the cross-sectional view following further definition ofthe plurality of layers 118 to produce the magnetoresistive device stack119. Such definition may be accomplished by one or more etching steps.Device stack 119 includes a plurality of layers that interact to formthe magnetoresistive device, which, for example, may be a MTJ device. Asdiscussed immediately above, in one embodiment, the photoresist isstripped prior to such etching, whereas in other embodiments, thephotoresist may be stripped at some point during the etching of thevarious layers included within the plurality of layers 118.

Following the definition of the magnetoresistive device stack 119, theelectrically conductive layer 110 is etched in order to form bottomelectrode 112, which is depicted in FIG. 8. The bottom electrode 112allows for an electrical connection to the bottom of themagnetoresistive device.

Notably, while described as appropriate for a magnetoresistive device,the two-step etching techniques described herein may also be useful inother devices in which defining an electrode using the combination ofisotropic and anisotropic etching, selective and non-corrosive etching,or some combination thereof, provides benefit. For example, devicesother than magnetoresistive devices may benefit from producing such atop electrode by first performing a main etch having a first level ofetching isotropy and then performing an over etch having a second levelof etching isotropy, where the first level of etching isotropy and thesecond level of etching isotropy are different. Similarly, devices otherthan magnetoresistive devices may benefit from producing a top electrodeby first performing a main etch having using a selective, corrosiveetching chemistry and then performing an over etch using a lesscorrosive chemistry.

FIGS. 9 and 10 provide cross-sectional views of the layers making upmagnetoresistive devices in specific embodiments in which the pluralityof layers 118 depicted in FIG. 1 are further detailed. As discussedabove with respect to FIG. 1, the layers shown in FIGS. 9 and 10 aredescribed in a general fashion, and may include multiple sub-layers aswell as composite layers. Thus, while FIGS. 9 and 10 include additionaldetail in order to provide further context for the embodiments discussedherein, they should not be viewed as limiting and rather as specificexamples to aid in illustration.

In the example shown in FIG. 9, the plurality of layers 118 used toproduce the magnetoresistive device stack 119 includes a lower layer ofmagnetic material 120, a dielectric layer 130, and an upper layer ofmagnetic material 140. In one embodiment, the dielectric layer 130serves as a tunnel barrier, which, in conjunction with magnetic materiallayers 120 and 140, establishes an MTJ structure. As noted above, eachof these layers may include multiple sub-layers. For example, lowerlayer of magnetic material 120 may include anti-ferromagnetic materialas well as other magnetic material layers arranged in a SAF structure,whereas the upper layer of magnetic material 140 may include multiplesub-layers that form a SYF structure.

FIG. 10 illustrates an alternate embodiment in which the plurality oflayers 118 used to produce the magnetoresistive device stack 119includes a different configuration of layers. The plurality of layers118 included in FIG. 10 includes a lower layer of magnetic material 220,a first dielectric layer 230, which may serve as a tunnel barrier, asecond upper layer of magnetic material 240, a second dielectric layer250, which may serve as a diffusion barrier, and a spacer layer 260. Aswas the case with the embodiments discussed above, each of these layersmay include a plurality of sub-layers as well as composite layers.

FIGS. 11-14 and 25-27 are flow charts that illustrate exemplaryembodiments of a method of manufacturing a magnetoresistive device,where, in one example, the magnetoresistive device is a spin-torque MTJdevice included in an MRAM. The operations included in the flow chartsmay represent only a portion of the overall process used to manufacturethe device. For example, FIGS. 11-12 and 25 focus on forming the topelectrode for the device from a set of already-formed layers using atwo-step etch process. The various tasks performed in connection withthe methods of FIGS. 11-14 and 25-27 may be performed by software,hardware, firmware, or any combination thereof. For illustrativepurposes, the following description of the methods in FIGS. 11-14 and25-27 may refer to elements mentioned above in connection with FIGS.1-10. In practice, portions of methods may be performed by differentelements of the described system, e.g., a processor, a display element,or a data communication component. It should be appreciated that methodsmay include any number of additional or alternative tasks, the tasksshown in FIGS. 11-14 and 25-27 need not be performed in the illustratedorder, and the methods may be incorporated into a more comprehensiveprocedure or process having additional functionality not described indetail herein. Moreover, one or more of the tasks shown in FIGS. 11-14and 25-27 could be omitted from an embodiment as long as the intendedoverall functionality remains intact.

In FIG. 11 the layers corresponding to the magnetoresistive device to beformed have already been deposited on an underlying substrate. At 302 apatterned layer of photoresist is formed over and electricallyconductive layer, where the electrically conductive layer provides thematerial used to form the top electrode for the magnetoresistive device.At 304, a first portion of the electrically conductive layer that is notcovered by the patterned layer of photoresist is etched. The etchingperformed at 304 utilizes an etching process that has a first level ofetching isotropy. At 306, a second portion of the electricallyconductive layer that is not covered by the patterned layer ofphotoresist is etched, where the second portion is etched using anetching process that has a second level of etching isotropy that isdifferent from the first level of etching isotropy used during theetching of the first portion at 304.

Thus, the etching operations corresponding to the top electrode aresplit into two separate etching steps that utilize differing levels ofisotropy. In one embodiment, the first etching step is an isotropic etchduring which further trimming of the photoresist occurs, whereas thesecond etching step is more anisotropic, thereby helping to clear awayresidual matter as well as providing sharp definition for themagnetoresistive device structure. In another embodiment, the firstetching operation may be an anisotropic etching operation such that thesharp definition is achieved, whereas the second etching step isisotropic.

When etching that is more anisotropic is desired, a greater bias powermay be applied during the etching operation whereas a lesser bias poweris applied during the isotropic etching. For example, the etching of thefirst portion at 304 may be accomplished using the same etchingchemistries as that used during the etching of the second portion at306, where a different amount of power is applied during the respectiveetching operations. If the etching of the first portion at 304 isisotropic and the etching of the second portion at 306 is moreanisotropic, a greater by a greater bias power may be applied during theetching of the second portion 306. As discussed above, applying greaterbias power may include applying the power to a chuck underlying thewafer during a plasma etching operation, where greater power to thechuck results in more directional flow of the plasma, thereby producinga more anisotropic etching operation.

While varying the power provides one means for adjusting the anisotropicnature of the etching operation, varying the pressure within the etchingchamber can also impact the istotropic/anisotropic nature of theetching. For example, applying a lesser amount of pressure during theetching of the second portion at 306 may increase the anisotropic natureof the etching by enabling the plasma to be more easily directed.Similarly, raising the pressure during the first etching operation at304 may cause the etching to be more isotropic as the plasma is forcedto interact with the material being etched from all sides and not in adirectional manner.

As was the case with FIG. 11, in FIG. 12 the various layers included andthe magnetoresistive device have already been formed prior to theoperations illustrated. At 312, a patterned layer of photoresist isformed over the electrically conductive layer, where the electricallyconductive layer provides the material from which the top electrode isto be formed. At 314 first portion of the electrically conductive layeris etched using a first bias power during a first plasma etch. Asdiscussed above, the first bias power can be controlled in order tocause the etching at 314 to be more or less anisotropic. At 316, asecond portion of the electrically conductive layer is etched using asecond bias power during a second plasma etch. Thus, differing biaspowers are used during the etching at 314 and 316 in order to achievedifferent levels of isotropy during the two-step etching process used toproduce the top electrode. Notably, the first and second etchingoperations at 314 and 316 may rely on the same etching chemistry, and,in one embodiment, the only difference between the two etching steps isthe amount of power applied to the chuck. Moreover, while the etching isdescribed as being separated into two distinct steps, in otherembodiments, the etching may be accomplished using a more gradualtransition between levels of isotropy. For example, rather than anabrupt shift in power from a lower level to a higher level, the powermay be gradually ramped up from an initial level to a greater level,thereby gradually increasing the anisotropic nature of the etch. Similargradual shifts in other parameters, including chemistry and pressure,may also be used to change the level of isotropy used while forming thetop electrode.

In FIG. 13, a patterned layer of photoresist is formed over a layer ofelectrically conductive material at 322, where the electricallyconductive material is to be processed to form the top electrode for themagnetoresistive device. At 324 a first portion of the electricallyconductive layer and portions of the patterned layer of layer ofphotoresist are etched using an isotropic etch. Thus, the isotropicnature of the etch at 324 not only removes portions of the electricallyconductive layer, but also helps to further trim the photoresist inorder to allow for smaller magnetoresistive devices that may not beachievable with conventional lithography and trimming techniques. Asdiscussed above, the isotropic nature of the etch at 324 may be achievedbased on a low bias power and higher pressure within the etchingchamber. A determination as to when to stop the etching performed at 324may be based on the amount of time or the detection of an endpointwavelength associated with the optical omission spectrum for the etchingoperation.

At 326 a second portion of the electrically conductive layer is etchedusing a more anisotropic etch. A determination as to when to stop theetching performed at 326 may be based on the amount of time or thedetection of an endpoint wavelength associated with the optical omissionspectrum for the etching operation. As discussed above, the moreanisotropic etch at 326 may be achieved by raising the power applied anddecreasing the pressure within the etching chamber. In one embodiment,the etching chemistry used in etching each of the first and secondportions at 324 and 326 is substantially similar. Thus, rather thanvarying the etching chemistry, the conditions present when the etchingoccurs can be manipulated in order to vary the isotropy of the etching.In other embodiments, a different etching chemistry may be employedduring the first and second etching portions 324 and 326 in order tovary the level of isotropy. As a result of the etching performed at 324and 326, the top electrode is formed. Thus, formation of the topelectrode has been split into at least two separate etching operations,where the first is an isotropic etch and the second is an anisotropicetch that helps to clear residual matter as well as provide sharpdefinition for the magnetoresistive device structure.

At 328 the patterned layer of photoresist is stripped using water vapor.Because the water vapor is non-reactive, the sidewalls of the topelectrode that have been exposed do not oxidize or degrade in some othermanner. At 330, subsequent layers below the top electrode are etched todefine the magnetoresistive device stack. As discussed above, etchingthe subsequent layers includes at least etching one or more layers ofmagnetic material and one or more dielectric layers that are not coveredby the top electrode to form the magnetic material stack. The topelectrode formed at 324 and 326 serves as a top electrical contact forthe magnetic material stack. As shown above with respect FIG. 10, thelayers underlying the top electrode may also include a spacer layer.Thus, the etching performed at 330 may include etching the portion ofthe spacer layer that is not covered by the top electrode. In someembodiments, the spacer layer may be formed of a reactive material suchthat it is helpful to stop the etching of the top electrode prior toreaching the material from which the spacer layer is formed.

At 332, a layer of electrically conductive material under themagnetoresistive device stack is etched to form the bottom electrode forthe magnetoresistive device. Thus, the stack structure is sandwichedbetween the top and bottom electrodes, which allow the device to beconnected to other circuitry for operation.

In FIG. 14 a plurality of magnetoresistive device layers are provided at342. The plurality of magnetoresistive device layers includes somelayers of magnetic material as well as the other various material layersdiscussed above as being included in the magnetoresistive device stack.At 344 an electrically conductive layer is formed over the plurality ofmagnetoresistive device layers. At 346 a hard mask is formed over theelectrically conductive layer. At 348 a patterned layer photoresist isformed over the hard mask layer. At 350, the hard mask layer is etchedto form a hard mask.

At 352 and 354 a two-step etching operation is employed to define thetop electrode for the magnetoresistive device. At 352 a first portion ofthe electrically conductive layer and portions of the patterned layer ofphotoresist are etched using a first etch. At 354 a second portion ofthe electrically conductive layer is etched using a second etch thatemploys increased power or pressure in order to increase the anisotropicnature of the etch.

At 356 the patterned layer photoresist is stripped using water vapor,and at 358 the subsequent layers below the top electrode are etched inorder to define the magnetoresistive device stack. At 360 anotherconductive layer underlying the magnetoresistive device stack is etchedin order to form the bottom electrode for the magnetoresistive device,thereby providing a top and bottom electrode with which externalcircuitry can access the magnetoresistive device.

In FIG. 25 the layers corresponding to the magnetoresistive device to beformed have already been deposited on an underlying substrate. At 502 apatterned layer of photoresist is formed over and electricallyconductive layer, where the electrically conductive layer provides thematerial used to form the top electrode for the magnetoresistive device.At 504, a first portion of the electrically conductive layer that is notcovered by the patterned layer of photoresist is etched. The etchingperformed at 304 utilizes a first etching chemistry. At 506, a secondportion of the electrically conductive layer that is not covered by thepatterned layer of photoresist is etched, where the second portion isetched using second etching chemistry that is different from the firstetching chemistry used during the etching of the first portion at 504.

Thus, the etching operations corresponding to the top electrode aresplit into two separate etching steps that utilize differingchemistries. In one embodiment, the first etching step may use a moreselective etch that is selective with respect to the material making upthe top electrode while minimizing erosion of the photoresist and anyhard mask that may be present. The second etching step may use achemistry that is less corrosive and does not harm the layers underlyingthe top electrode such as those included in the magnetoresistive stackfor the device. The second etching step may be less selective andtherefore cause some amount of erosion of the photoresist and any hardmask, but if the second etching step is only used to remove a limitedamount of the layer of conductive material the erosion can be kept totolerable levels. It should be appreciated that the point at whichetching using the first chemistry stops and etching using the secondchemistry begins can be selected based on a number of parameters,including, for example, the level of erosion of the photoresist and anyhard mask which is tolerable, and the susceptibility of the underlyinglayers to the corrosiveness of the first chemistry.

As noted above, suitable chemistries for the first etching 504 includechlorine based chemistries. Another option for a more selective etchingchemistry is one that includes hydrogen bromide. Less corrosivechemistries suitable for the second etching 506 include fluorine basedchemistries. As also mentioned above, determining when to stop each ofthe first etching 504 and the second etching 506 can be based on anamount of time or detection of an endpoint wavelength.

In FIG. 26, a patterned layer of photoresist is formed over a layer ofelectrically conductive material at 522, where the electricallyconductive material is to be processed to form the top electrode for themagnetoresistive device. At 524 a first portion of the electricallyconductive layer is etched using a first etching chemistry. As discussedabove, the first etching chemistry at 524 may be a corrosive, selectivechemistry. For example the first etching chemistry may have an etch ratefor the electrically conductive layer that is at least three timesgreater than the etch rate of the first chemistry with respect to thephotoresist. A determination as to when to stop the etching performed at524 may be based on the amount of time or the detection of an endpointwavelength associated with the optical omission spectrum for the etchingoperation.

At 526 a second portion of the electrically conductive layer is etchedusing a second etching chemistry that is different than the firstetching chemistry. A determination as to when to stop the etchingperformed at 526 may be based on the amount of time or the detection ofan endpoint wavelength associated with the optical omission spectrum forthe etching operation. As discussed above, the second etching chemistrymay be a less corrosive chemistry that avoids damaging any layersunderlying the layer of conductive material as it removes any remainingportions of the conductive material.

At 528 the patterned layer of photoresist is stripped using water vapor.Because the water vapor is non-reactive, the sidewalls of the topelectrode that have been exposed do not oxidize or degrade in some othermanner. At 530, subsequent layers below the top electrode are etched todefine the magnetoresistive device stack. At 532, a layer ofelectrically conductive material under the magnetoresistive device stackis etched to form the bottom electrode for the magnetoresistive device.Thus, the stack structure is sandwiched between the top and bottomelectrodes, which allow the device to be connected to other circuitryfor operation.

In FIG. 27 a plurality of magnetoresistive device layers are provided at542. The plurality of magnetoresistive device layers includes somelayers of magnetic material as well as the other various material layersdiscussed above as being included in the magnetoresistive device stack.At 544 an electrically conductive layer is formed over the plurality ofmagnetoresistive device layers. At 546 a hard mask is formed over theelectrically conductive layer. At 548 a patterned layer photoresist isformed over the hard mask layer. At 550, the hard mask layer is etchedto form a hard mask.

At 552 and 554 a two-step etching operation is employed to define thetop electrode for the magnetoresistive device. At 552 a first portion ofthe electrically conductive layer is etched using a first etch. At 554 asecond portion of the electrically conductive layer is etched using asecond etch that employs different parameters than the first etch. Thus,while the first etch may use a first power level, a first pressurelevel, and a first chemistry, the second etch may use a second powerlevel, a second pressure level, and a second chemistry, where one ormore of the parameters for the second etch is different from that usedin the first etch. In such a manner the first etch can be more or lessanisotropic, more or less selective with respect to certain materials,and more or less corrosive to certain materials than the second etch.

At 556 the patterned layer photoresist is stripped, which may be doneusing water vapor. At 558 the subsequent layers below the top electrodeare etched in order to define the magnetoresistive device stack. At 560another conductive layer underlying the magnetoresistive device stack isetched in order to form the bottom electrode for the magnetoresistivedevice, thereby providing a top and bottom electrode with which externalcircuitry can access the magnetoresistive device.

FIGS. 15-21 provide cross-sectional views of the various layers makingup a magnetoresistive device and illustrate the stages of deviceformation during which the various layers are etched. The layersincluded in the magnetoresistive device illustrated in FIGS. 15-21correspond to those discussed earlier with respect to FIG. 10. Notably,the layers included in the magnetoresistive device illustrated in FIGS.15-21 include a spacer layer 260 under the electrically conductive layer150 used to form the top electrode.

As shown in FIG. 15, the layers included in the device are deposited ona substrate 102. A lower electrically conductive layer 110 is formedover the substrate 102, a lower layer of magnetic material 220 is formedover the electrically conductive layer 110, a lower dielectric layer 240is formed over the lower layer of magnetic material 220, an upper layerof magnetic material 240 is formed over the lower dielectric layer 230,an upper dielectric layer 250 is formed over the upper layer of magneticmaterial 240, a spacer layer 260 is formed over the upper dielectriclayer 250, the electrically conductive layer 150 is formed over thespacer layer 260, a hard mask layer 160 is formed over the electricallyconductive layer 150 and etched to form hard mask 162, and patternedphotoresist 170 is formed over the hard mask layer 160 and trimmed toform trimmed photoresist 172. As shown in FIG. 15, after the patternedlayer of photoresist has been formed and trimmed, the hard mask layernot covered by the patterned layer of photoresist is etched to form hardmask 162.

In FIG. 16, the top layer of electrically conductive material 150 hasbeen etched to form top electrode 155. The etching performed in order torealize top electrode 155 may include the two-step etch processdiscussed above, other known techniques for etching to form a topelectrode, as well as techniques later developed for top electrodeformation.

FIG. 17 provides a cross-sectional view of the layers from FIG. 16following the stripping of the patterned layer of photoresist. As notedabove, removing the photoresist prior to etching the layers included inthe magnetoresistive device is beneficial as it ensures that subsequentat steps are not contaminated by the photoresist material, which isprone to breakdown and can leave behind undesirable residual material.Because the sidewalls of the top electrode 155 have been exposed by theetching process prior to removal of the photoresist, it is desirable tostrip the patterned layer of photoresist using a non-oxidizing gas.Using a non-oxidizing gas to strip the photoresist prevents oxidation orother degradation of the sidewalls of the top electrode 155 and alsoprevents oxidation or other degradation of the spacer layer 260 prior toetching of that layer. In other embodiments, the photoresist may bestripped at a later point in time, such as during or after etching ofone or more of the layers included in that magnetoresistive devicestack. In such embodiments, stripping the photoresist using anon-reactive gas is also beneficial in preventing degradation of thesidewalls or other portions of those layers that are exposed when thephotoresist is stripped.

By avoiding oxidation or other degradation of the layers within themagnetoresistive device, problems such as higher switching voltages andincreased variance in switching voltages across many devices included ina memory or other device are avoided. For example, oxidation may resultin a roughness along the sidewalls of the top electrode, where thatroughness translates into non-ideal subsequent etching stepscorresponding to the layers below the top electrode. In addition topreventing oxidation or degradation of the exposed material in thevarious layers when photoresist is stripped, using a non-reactive gas tostrip the photoresist can also provide beneficial passivation to theexposed layers, thereby helping to avoid degradation of those layersduring subsequent etching steps. Moreover, the etching utilized to formthe top electrode is typically chemical in nature, and the non-reactivegas (e.g. water vapor) helps to eliminate the corrosive chemistries usedduring formation of the top electrode prior to the etching stepscorresponding to the various layers within the magnetoresistive devicestack. Because of the benefits of passivation and elimination ofcorrosive chemistries, even if the photoresist stripping is performedusing something other than a non-oxidizing gas, it can be useful toexpose the various layers to water vapor in order to realize thosebenefits.

In one embodiment, the non-oxidizing gas used strip the photoresist iswater vapor (H₂O), and the stripping is performed with no cathode biasapplied during the stripping process. In other embodiments, othernon-reactive gases may be used, where some examples include carbontetrafluoride (CF₄), carbon trifluoride (CHF₃), and a mix of water vaporand one or more non-reactive gases.

FIG. 18 illustrates a cross-sectional view corresponding to FIG. 17after the spacer layer 260 has been etched to form etched spacer layer262. The etched spacer layer 262 acts as a diffusion barrier, andprevents diffusion of the material making up the top electrode 155 fromintermingling with or reacting with the dielectric layer 250 underlyingthe spacer layer. Thus, the spacer layer 262 isolates the underlyingdielectric layer from the top electrode. As noted above, while thefigures show the photo resist having been removed prior to etching thespacer layer 260, the photoresist can be stripped at different timesduring the manufacturing process, and, therefore, if such strippingoccurs after the spacer layer has been etched, using a non-reactive gassuch as water vapor to strip the photoresist will help prevent oxidationor other degradation of the spacer layer.

In some embodiments, the spacer layer includes ruthenium (Ru), which isvery reactive with oxygen. As such, using a non-reactive gas to stripthe photoresist would prevent oxidation of any exposed portion of thespacer layer. However, following etching of the spacer layer 260,further etching steps corresponding to the underlying dielectric andmagnetic layers may also result in oxidation or other degradation of thespacer layer. For example, the dielectric layer 250 and underlyinglayers may be etched using argon/oxygen etch chemistry (mixtures of Arand O₂) that reacts with ruthenium, causing it to oxidize and expandoutwards from the sidewalls forming “veils.” As such, utilizing anon-reactive material for the spacer layer that does not reactive toetching materials used is beneficial in that it avoids any oxidationproblems corresponding to the various etchings performed in devicemanufacture. For example, ruthenium dioxide (RuO₂), palladium oxide(PdO₂), iridium oxide (IrO₂), PtMn, IrMn, or other noble metals andalloys that will not oxidize can be used for the spacer layer.

Avoiding the oxidation prevents roughness on the sidewalls of the spacerlayer, thereby helping to ensure precise and accurate etching of thelayers underlying the spacer layer. If such oxidation is allowed tooccur, bulging sidewalls of the spacer layer may result, therebyimpacting the underlying etch steps and device functionality. Suchirregularities induced by the oxidation can impact MTJ device switchingcharacteristics in a negative manner, for example by increasing thevariance in terms of device switching characteristics across the device.

Another technique for avoiding oxidation of the spacer layer is to omitthe spacer layer from the device structure. Omitting the spacer layerensures that any disadvantages caused by roughness on the sidewalls ofthe spacer layer are avoided.

FIG. 19 shows a cross-sectional view corresponding to that of FIG. 18following etching of the top dielectric layer 250 resulting in etchedtop dielectric layer 252. The top dielectric layer may serve as adiffusion barrier within the magnetoresistive device. In one embodiment,the top dielectric layer includes magnesium oxide. In some embodiments,in order to protect the spacer layer 262 and top dielectric layer 252following their etching, encapsulation of the sidewalls of those layersmay be performed. Details regarding such encapsulation can be found inU.S. Pat. No. 8,685,756, which is assigned to the same assignee as thepresent application and is incorporated by reference herein. If thespacer layer and dielectric layer are encapsulated following theirdefinition by etching, subsequent oxidation of those layers isprevented, thereby ensuring the layers remain intact and rough sidewallsdo not appear.

As shown in FIG. 20, following etching of the top dielectric layer 250,the upper magnetic material layer 240 is etched to form layer 242 of themagnetoresistive device stack. As noted above, if the etched sidewallsof the dielectric layer 252 and spacer layer 262 are encapsulated priorto etching the magnetic layer 240, oxidation of the dielectric layer 252and spacer layer 262 will not occur. As also shown in FIG. 20, the lowerdielectric layer 230 is etched to provide etched dielectric layer 232,and the lower magnetic material layer 220 is etched to form etchedmagnetic material layer 222. After etching, these layers may also beencapsulated in order to protect them during subsequent etching steps,including, for example, etching a lower layer of antiferromagneticmaterial or etching the lower layer of electrically conductive material110 to form the bottom electrode. Encapsulation of the etched dielectriclayer 232, which may correspond to a tunnel junction for the device, andthe etched magnetic material layer 222 is discussed in detail in relatedpending U.S. Patent Application number <AA/BBB,CCC> entitled “Isolationof Magnetic Layers During Etch in a Magnetoresistive Device” havingattorney docket number 080.0466 and listing Chaitanya Mudivarthi, SarinA. Deshpande, and Sanjeev Aggarwal as inventors, which is incorporatedby reference herein.

As shown in FIG. 21, following definition of the magnetoresistive devicestack, the bottom electrode 112 is formed from the lower level ofelectrically conductive material 110. The lower electrode 112 provides ameans to electrically contact the magnetoresistive device stack. Inaddition, FIG. 21 shows that the etched hard mask 162 has been removed,thereby providing access to the top electrode 155.

Thus, in magnetoresistive devices that include one or more spacerlayers, disadvantages arising from the reactivity of the material in thespacer layers can be avoided by using non-reactive material for thespacer layer in place of reactive material. In other embodiments, spacerlayers may be omitted from the device structure. As also described,stripping photoresist using non-reactive gases such as water vapor canbe employed for a portion of the manufacturing process, thereby avoidingoxidation of electrode sidewalls and spacer layers that are reactive,while also providing benefits in terms of passivating other exposedsurfaces. Moreover, in order to avoid oxidation or other reactionsduring later etching operations, reactive spacer layers and dielectriclayers can be encapsulated, thereby protecting them during thosesubsequent etching operations.

FIGS. 22-24 are flow charts that illustrate exemplary embodiments of amethod of manufacturing a magnetoresistive device, where, in oneexample, the magnetoresistive device is an MTJ device used in an MRAM.The operations included in the flow charts may represent only a portionof the overall process used to manufacture the device. The various tasksperformed in connection with methods in FIGS. 22-24 may be performed bysoftware, hardware, firmware, or any combination thereof. Forillustrative purposes, the following description of the methods in FIGS.22-24 may refer to elements mentioned above in connection with FIGS.1-10 and 15-21. In practice, portions of methods may be performed bydifferent elements of the described system, e.g., a processor, a displayelement, or a data communication component. It should be appreciatedthat methods may include any number of additional or alternative tasks,the tasks shown in FIGS. 22-24 need not be performed in the illustratedorder, and the methods may be incorporated into a more comprehensiveprocedure or process having additional functionality not described indetail herein. Moreover, one or more of the tasks shown in FIGS. 22-24could be omitted from an embodiment as long as the intended overallfunctionality remains intact.

In FIG. 22 a patterned layer of photoresist is formed at 402 over afirst electrically conductive layer. As discussed and illustrated above,a hard mask layer may be included between the patterned layer ofphotoresist and the electrically conductive layer, thereby providing fora hard mask defined by the patterned layer of photoresist, where thehard mask may be used for subsequent etching steps. At 404 the firstelectrically conductive layer is etched to form a first electrode. Theetching utilized to form the first electrode may include the two-stepetching process discussed above, or other conventional or laterdiscovered techniques for forming such an electrode. At 406, thepatterned layer photoresist is stripped using a non-oxidizing gas, suchas water vapor. By stripping the patterned layer photoresist using anon-oxidizing gas prior to further processing of the underlying layers,the photoresist is removed in a manner that does not result in oxidationof the sidewalls of the first electrode. As noted above, it is desirableto remove the photoresist before physical etching in which bombardmentof the wafer occurs, as such physical etching degrades the photoresistin a manner that interferes with the etching process. In addition toeliminating the patterned layer of photoresist, the stripping usingwater vapor can also provide advantages in terms of passivation andremoval of unwanted material left over from chemical etch processesassociated with definition of the first electrode.

In FIG. 23 a first dielectric layer is formed at 412. As described andillustrated with respect to FIGS. 15-21, the dielectric layer formed at412 may correspond to the top dielectric layer 250. At 414, a spacerlayer is formed adjacent to the first dielectric layer, where the spacerlayer is formed using a non-reactive material. As noted above, by usinga non-reactive material for the spacer layer, problems associated withspacer layer reacting to various etch chemistries are avoided. At 416, afirst electrically conductive layer is formed adjacent to the spacerlayer such that spacer layer is between the first dielectric layer andthe first electrically conductive layer. The first electricallyconductive layer provides the material later etched to produce the topelectrode. Following the formation steps shown in FIG. 23, the etchingsteps discussed above can occur in order to define the magnetoresistivedevice structure, where the resulting magnetoresistive device includes anon-reactive spacer layer.

FIG. 24, which includes FIGS. 24A and 24B, provides a flow chart of theformation of the various layers and their subsequent etching in theproduction of a magnetoresistive device. At 422 a bottom electricallyconductive layer is formed over a substrate, where the bottomelectrically conductive layer will later be etched in order to form abottom electrode. At 424 a lower layer of magnetic material is formedover the bottom electrically conductive layer. The lower layer ofmagnetic material may include a plurality of layers, where one or moreof the layers include magnetic material. For example, in one embodiment,the lower layer of magnetic material may include a plurality of layersthat form a SAF structure following subsequent processing steps. At 426a lower dielectric layer is formed over the lower layer of magneticmaterial. The lower dielectric layer may serve as a tunnel junction inan MTJ device.

At 428 an upper layer of magnetic material is formed over the lowerdielectric layer. As was the case with the lower layer of magneticmaterial, the upper layer of magnetic material may include a pluralityof sub-layers, where some of the sub-layers are magnetic materials,whereas others may be coupling layers that force certain interactionsbetween the layers of magnetic material. For example, the upper layer ofmagnetic material may include layers that, after subsequent processing,result in a SYF structure. At 430, and upper dielectric layer is formedover the upper layer of magnetic material. In one embodiment, the upperdielectric layer serves as a diffusion barrier. At 432, a spacer layeris formed over the upper dielectric layer. As discussed above, thespacer layer may prevent diffusion between the top electrode of thedevice and the upper dielectric layer. As also discussed above, thespacer layer may be formed of a non-reactive material in order to avoidundesirable rough edges of the spacer layer resulting from reactionsduring subsequent etching operations. In other embodiments, the spacerlayer may be omitted from the device structure.

At 434 a top electrically conductive layer is formed over the spacerlayer. The top electrically conductive layer provides the material usedto define the top electrode for the device. At 436, a hard mask layer isformed over the top electrically conductive layer. At 438, a patternedlayer of photoresist is formed over the hard mask layer. At 440, thepatterned layer of photoresist is trimmed in order to reduce the featuresize of the photoresist. As noted above, such trimming enables finerresolution than may be achieved using available lithographic techniques.At 442 the hard mask layer is etched to define a hard mask. At 444 theupper electrode layer not covered by the hard mask layer is etched toform the top electrode.

At 446 the patterned layer of photoresist is stripped using anon-oxidizing gas such as water vapor. As noted above, stripping thephotoresist may occur immediately after definition of the top electrode,or at other times during the wafer processing operations correspondingto manufacture of the magnetoresistive device. For example, some or allof the spacer layer may be etched prior to stripping the patterned layerof photoresist. At 448 the spacer layer is etched. At 450 the upperdielectric layer is etched, thereby exposing the sidewalls of the upperdielectric layer and rendering them vulnerable to oxidation or otherundesirable reactive chemistries. In order to avoid such oxidation, at452 the sidewalls of the etched upper dielectric layer are encapsulated.Encapsulation prevents oxidation or other undesirable reactions fromoccurring to the sidewalls of the upper dielectric layer. As notedabove, the encapsulation performed at 452 may also include encapsulationof the sidewalls of the spacer layer.

At 454 each of the layers formed under the upper dielectric layer isetched to form the magnetoresistive device. Thus, one or multipleetching operations corresponding to the various underlying layers occurin order to define the magnetoresistive device stack and bottomelectrode. By minimizing undesirable degradation of sidewalls includedin the magnetoresistive device structure, the precision with which thedevices can be made is improved, thereby risk reducing the variance ofswitching characteristics or other MTJ parameters across the die, whichmay correspond to an MRAM device.

Although the described exemplary embodiments disclosed herein aredirected to various magnetoresistive-based devices and methods formaking same, the present disclosure is not necessarily limited to theexemplary embodiments, which illustrate inventive aspects that areapplicable to a wide variety of semiconductor processes and/or devices.Thus, the particular embodiments disclosed above are illustrative onlyand should not be taken as limitations, as the embodiments may bemodified and practiced in different but equivalent manners apparent tothose skilled in the art having the benefit of the teachings herein.Accordingly, the foregoing description is not intended to limit thedisclosure to the particular form set forth, but on the contrary, isintended to cover such alternatives, modifications and equivalents asmay be included within the spirit and scope of the inventions as definedby the appended claims so that those skilled in the art shouldunderstand that they can make various changes, substitutions andalterations without departing from the spirit and scope of theinventions in their broadest form.

What is claimed is:
 1. A method of manufacturing amagnetoresistive-based device, comprising: forming a patterned layer ofphotoresist over an electrically conductive layer; etching, using afirst etching chemistry, a first portion of the electrically conductivelayer not covered by the patterned layer of photoresist; and etching,using a second etching chemistry, a second portion of the electricallyconductive layer not covered by the patterned layer of photoresist,wherein the first etching chemistry is different than the second etchingchemistry.
 2. The method of claim 1, wherein the first etching chemistryis more selective with respect to the electrically conductive layer thanthe second etching chemistry.
 3. The method of claim 2, wherein thefirst etching chemistry has an etch rate for the electrically conductivelayer that is at least three times greater than an etch rate for thepatterned layer of photoresist.
 4. The method of claim 2, wherein thefirst etching chemistry is chlorine based.
 5. The method of claim 2,wherein the first etching chemistry includes hydrogen bromide.
 6. Themethod of claim 2, wherein the second etching chemistry is fluorinebased.
 7. The method of claim 1, wherein etching the second portion ofthe electrically conductive layer using the second etching chemistryfurther comprises etching the second portion using a non-corrosiveetching chemistry.
 8. The method of claim 7, wherein the non-corrosiveetching chemistry is less reactive with layers underlying theelectrically conductive layer than the first etching chemistry used toetch the first portion of the electrically conductive material.
 9. Themethod of claim 8, wherein etching the first and second portions of theelectrically conductive layer forms a top electrode, and wherein themethod further comprises: etching a layer of magnetic material notcovered by the top electrode to form a magnetic material stack, whereinthe layer of magnetic material underlies the layer of conductivematerial, and wherein the non-corrosive etching chemistry is lessreactive with the layer of magnetic material than the first etchingchemistry.
 10. The method of claim 8, wherein the non-corrosive etchingchemistry is less selective than the first etching chemistry used toetch the first portion of the electrically conductive material.
 11. Themethod of claim 1, wherein etching the first portion of the electricallyconductive layer further comprises stopping etching the first portionbased on one of an amount of time and detection of an endpointwavelength.
 12. The method of claim 1, wherein etching the secondportion of the electrically conductive layer further comprises stoppingetching the first portion based on one of an amount of time anddetection of an endpoint wavelength.
 13. A method of manufacturing amagnetoresistive based device, comprising: providing a plurality ofmagnetoresistive device layers, the plurality of magnetoresistive devicelayers including a plurality of layers of magnetic material; forming anelectrically conductive layer over the plurality of magnetoresistivedevice layers; forming a hard mask layer over the electricallyconductive layer; forming a patterned layer of photoresist over the hardmask layer; etching the hard mask layer not covered by the patternedlayer of photoresist to form a hard mask; etching a first portion of theelectrically conductive layer not covered by the hard mask, whereinetching the first portion of the electrically conductive layer uses afirst etching chemistry; etching a second portion of the electricallyconductive layer not covered by the hard mask, wherein etching thesecond portion of the electrically conductive layer uses a secondetching chemistry that is different from the first etching chemistry;and etching at least a portion of the plurality of magnetoresistivelayers not covered by the hard mask to form a magnetic material stack.14. The method of claim 13, wherein the first portion of theelectrically conductive layer is greater than the second portion of theelectrically conductive layer.
 15. The method of claim 14, wherein thefirst etching chemistry is more selective with respect to theelectrically conductive layer than the second etching chemistry.
 16. Themethod of claim 15, wherein the first etching chemistry is morecorrosive than the second etching chemistry.
 17. The method of claim 15,wherein etching at least a portion of the plurality of magnetoresistivelayers not covered by the hard mask uses a third etching chemistry,wherein second etching chemistry is less reactive with the at least aportion of the plurality of magnetoresistive layers than the firstchemistry.
 18. The method of claim 14, wherein the first etchingchemistry is chlorine based.
 19. The method of claim 14, wherein thesecond etching chemistry is fluorine based.
 20. The method of claim 14,wherein the first etching chemistry has an etch rate for theelectrically conductive layer that is at least three times greater thanan etch rate for the patterned layer of photoresist.